Systems and methods for implantable leadless spine stimulation

ABSTRACT

Systems and methods are disclosed to stimulate spine tissue to treat medical conditions such as pain and spinal injury. The invention uses electrical stimulation of the spine, where vibrational energy from a source is received by an implanted device and converted to electrical energy and the converted electrical energy is used by implanted electrodes to stimulate the pre-determined brain site. The vibrational energy is generated by a controller-transmitter, which could be located either externally or implanted. The vibrational energy is received by a receiver-stimulator, which could be located in the various regions on around the spine. The implantable receiver-stimulator stimulates different locations in the spine region to provide therapeutic benefit.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 11/764,574, now U.S. Pat. No. 7,899,542, filed Jun. 18, 2007, whichclaims the benefit of provisional U.S. Application No. 60/805,315, filedJun. 20, 2006, the full disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The systems and methods of this invention relate to direct electricalstimulation of nerve tissue in the spinal cord or spinal column fortreatment of pain due to a variety of medical conditions. Specifically,the present invention relates to methods and apparatus for applying suchstimulation without the use of conventional lead/electrode systems.

2. Description of the Background Art

Electrical stimulation of spinal nerve roots, the spinal cord, and/orother nerve bundles in the region of the spine, for the purpose ofchronic pain management, has been actively practiced since the 1960s.Application of an electrical field to nerve tissue in the spine (i.e.,spinal nerve roots and spinal cord bundles) is known to effectivelyinterfere with the transmission of pain signals to the brain. Theseapplications are done today both with externally applied devices andimplanted devices. Applying specific electrical pulses to spinal nervoustissue or to peripheral nerve fibers that corresponds to regions of thebody afflicted with chronic pain can induce paresthesia, or a subjectivesensation of numbness or tingling, or can in effect block paintransmission to the brain from the pain-afflicted regions. Depending onthe individual patient, paresthesia can effectively “mask” certain painsensations to the brain. Treatment regimens and targeted spinallocations are known in related art through use of current, commonstimulation devices and methods. Commonly implanted devices for spinalnerve stimulation are made by such companies as Medtronic, AdvancedNeuromodulation Systems, Advanced Bionics, and others.

The spine is an anatomical structure that consists of bones (vertebrae),cartilage (discs), and the spinal cord (a nervous system structure thatgenerally bundles or collects various nerves connecting peripheral areasof the body to the brain). As illustrated in FIG. 1 the spine is dividedinto five regions: (i) cervical (neck), (ii) thoracic (mid-back), (iii)lumbar (lower back), (iv) sacrum, and (v) coccyx (tailbone). Theperipheral nervous system refers to the cervical, thoracic, lumbar, andsacral nerve trunks leading away from the spine to all regions of thebody. The peripheral nervous system also includes cranial nerves. Painsignals travel between the brain and to other regions of the body usingthis network of nerves that all travel along the spine as part of thespinal cord.

Transcutaneous electrical nerve stimulation (TENS) is a well knownmedical treatment used primarily for symptomatic relief and managementof chronic intractable pain and as an adjunctive treatment in themanagement of post surgical and post traumatic acute pain. TENS involvesthe application of electrical pulses to the skin of a patient, whichpulses are generally of a low frequency and are intended to affect thenervous system in such a way as to suppress the sensation of pain, inthe area that the electrodes are applied. This typically would beindicated for use in acute or chronic injury or otherwise used as aprotective mechanism against pain. Typically, two electrodes are securedto the skin at appropriately selected locations. Mild electricalimpulses are then passed into the skin through the electrodes tointeract with the nerves lying thereunder. As a symptomatic treatment,TENS has proven to effectively reduce both chronic and acute pain ofpatients.

Spinal Cord Stimulation (SCS) generally refers to treatments for avariety of medical conditions that apply electrical stimulation directlyon nerves, nerve roots, nerve bundles, tissue or regions of the spine.Currently available stimulator systems for SCS are fully implantedelectronic devices placed subcutaneously under the skin and connectedvia insulated metal lead(s) to electrodes which are invasively insertedinto or onto the nerves or close to the nerves or spinal cord region. Acommonly implanted SCS system contains a battery to power the system.Some implanted SCS systems use an RF wireless connection instead of abattery to power the implanted device. In these RF systems, a receiverdevice is implanted subcutaneously and a transmitter is worn on theoutside of the body. The antenna are tuned to each other and alignedsuch that control information and power is transmitted to the receiver,which then directs the electrical impulses to the electrodes through theleads. The external transmitter contains batteries to power thetransmission. All systems have the capability to externally adjustsettings of the implanted system through a programming device.

In SCS and TENS systems, electrical energy is delivered through leadwires to the electrodes. For SCS, implanted electrodes are positionedexternal to a patient's dura layer (epidural), a structure thatsurrounds the spinal cord. SCS uses the implanted electrodes to delivera variety of stimulation modalities with the electric pulse waveformdefined by a plurality of variables, including: pulse width, pulsefrequency (Hz) or duty cycle, amplitude (V), and sometimes waveformshape (e.g. mono-phasic or bi-phasic).

SCS is used for treatment of headache, migraine headache, or facial painby stimulating spinal cord including the trigeminal ganglion or ganglia,a trigeminal nerve(s), a branch(es) of a trigeminal nerve(s) (e.g., anophthalmic nerve(s), a maxillary nerve(s), and/or a mandibularnerve(s)), or a branch(es) of any of these neural structures.

SCS is used for the treatment of chronic pelvic pain due to suchconditions as lumbosacral radiculitis, lumbosacral radiculopathy,lumbosacral plexitis, lumbosacral plexopathy, vulvadynia, coccygodynia,peripheral neuritis, and peripheral neuropathy, by applying stimulationto the epidural space of the sacrum on or near selected sacral nerveroots.

SCS is used for chronic pain associated with injury to the spine such asherniated discs or compression fractures. SCS is also used for treatingsevere chronic pain of a nonspecific origin. Stimulation of nerve tissuein a variety of spinal areas is known to reduce symptoms and enhance thequality of life in patients with chronic pain.

As described above, TENS and SCS devices are battery-powered electronicdevices either used transcutaneously (TENS) or implanted (SCS) andconnected via insulated metal lead(s) to electrodes which are eitherplaced on the skin (TENS) over the spine or implanted into the dura orepidural layer of the spine (SCS). The implanted electrodes for SCS arepositioned on leads that are placed percutaneously, through needlepunctures, or through minimally invasive surgical procedures suchlaminectomy methods, or through direct surgical access to position theelectrodes into epidural regions of the spine. Multiple electrodestypically between 4 and 16 are available on the lead and are positionedin the region that is targeted for electrical stimulation. The implantedleads are then subcutaneously tunneled to the pulse generator (alsoreferred to as a controller) that is implanted in a subcutaneous pocket.The use of these lead wires is associated with significant problems suchas complications due to infection, lead failure, lead migration, andelectrode/lead dislodgement.

Many attempts to overcome the complications and limitations imposed bythe use of electrical leads have been reported. For example,self-contained implantable microstimulators and remotely poweredmicrostimulators have been described; however each approach suffers fromsome significant limitation. A self-contained microstimulator mustincorporate a battery or some other power supply; this imposesconstraints on size, device lifetime, available stimulation energy, orall three. Due to high use or high energy requirements of thetherapeutic stimulation some SCS devices contain recharageable batteriesor are powered remotely with an RF coupling to the controller.

For leadless solutions in other similar stimulation applications,remotely powered devices have previously utilized either radiofrequency(RF) or electromagnetic transformer power transmission. RF energytransmission, unless the transmitting and receiving antennae are placedin close proximity, suffers from inefficiency and limited safe powertransfer capabilities, limiting its usefulness in applications whererecharging or stimulation must be accomplished at any significant depth(>1-2 cm) within the body, in particular where it is desired topermanently implant both the transmitter and receiver-stimulator.Electromagnetic coupling can more efficiently transfer electrical power,and can safely transfer higher levels of power (devices with capacity inexcess of 20 Watts have been produced) but again relies on closeproximity between transmitting and receiving coils, or the utilizationof relatively large devices for deeper (5-8 cm maximum) implantation.

The methods and apparatus of the current invention utilize vibrationalenergy, particularly at ultrasonic frequencies, to overcome many of thelimitations of currently known solutions for SCS and TENS, by achievinga spinal cord stimulation capability without the use of leads connectedto a stimulation controller/pulse generator.

The following patents, all of which are incorporated in this disclosurein their entirety, describe various aspects of using electricalstimulation for achieving various beneficial effects. U.S. Pat. No.3,835,833 titled “Method for Obtaining Neurophysiological Effects” byLimoge describes delivery and parameters for electrical stimulation in aTENS stimulation system. U.S. Pat. No. 4,690,144 titled “WirelessTranscutaneous Electrical Tissue Stimulator” by Rise et al. alsodescribes delivery, systems, and application parameters for a TENSstimulation system. U.S. Pat. No. 6,735,475 titled “Fully implantableminiature neurostimulator for stimulation as a therapy for headacheand/or facial pain” by Whitehurst et al. describes an implantablemicrostimulator used for treatment of pain in peripheral nervesgenerally in the skull or the cervical regions of the spine. U.S. Pat.No. 6,748,276 titled “Neuromodulation therapy system” by Daignault etal. describes an implantable SCS system that uses an external RFcommunication to adjust delivery of therapy. U.S. Pat. No. 6,027,456titled “Apparatus and method for positioning spinal cord stimulationleads” by Feler et al. describes approaches to the implantation of leadsinto the dorsal column of a patient. U.S. Pat. No. 5,938,690 titled“Pain management system and method” by Law et al. describes methods fordetermining and optimizing treatment parameters and regimens for bymapping patient responses to test stimulation patterns. U.S. Pat. No.6,002,965 titled “Epidural nerve root stimulation” by Feler et al.describes treating pelvic pain by application of stimulation in thesacral and lumbar regions of the spine. U.S. Pat. No. 5,405,367 titled“Structure and Method of Manufacture of an Implantable Microstimulator”by Schulman et al. describes an implantable microstimulator usedgenerally for stimulation of tissue. U.S. Pat. No. 6,037,704 titled“Ultrasonic Power Communication System” by Welle describes the use ofultrasound energy transfer from a transmitter to a receiver for purposesof powering a sensor or actuator without being connected by a lead/wire.U.S. Pat. No. 6,366,816 titled “Electronic Stimulation Equipment withWireless Satellite Units” by Marchesi describes a tissue stimulationsystem based on a wireless radio transmission requiring the charging ofa battery at the receiver and separate command signals used to controlthe delivery of stimulation. German patent application DE4330680A1titled “Device for Electrical Stimulation of Cells within a Living Humanor Animal” by Zwicker describes a general approach to power transferusing acoustic energy for tissue stimulation.

BRIEF SUMMARY OF THE INVENTION

This invention relates to methods and devices for using electricalstimulation of spinal cord nerves and regions of the spinal cord as atreatment for pain, particularly chronic pain using vibrational energyas a means to transmit energy and signal information from a firstdevice, to a second device containing means to receive such vibrationalenergy and converting it into electrical energy and then apply thatelectrical energy to stimulating electrodes. The first device isintended to be either implanted or to be used externally. The seconddevice is intended to be either permanently or temporarily implantedwith stimulating electrodes in close proximity to the tissue or nerveregion to be stimulated.

This application of leadless electrical stimulation is for spinal cordstimulation purposes, where the stimulation acts on the nerves to reducepain. The invention is a system comprising a controller-transmitter, animplanted receiver-stimulator, a programmer to adjust therapyparameters, and stimulation electrodes, such that the stimulationelectrodes would be in contact with tissue in the spine regions, inclose proximity to the tissue or region to be stimulated to facilitatetreatment. Systems incorporating the concepts presented have advantagesover currently available devices, particularly by eliminating therequirement for electrical leads, and by providing the capability forsimultaneous or sequenced stimulation of multiple sites.

In one embodiment, the controller-transmitter is implanted. Thecontroller-transmitted is implanted subcutaneously beneath the skin. Inanother embodiment, the controller-transmitter is applied on theexternal surface of the skin. The transmitted vibrational energy isdirected to the receiver-stimulator to cause electrical stimulation atthe electrodes of the receiver-stimulator.

In one use of the external embodiment of the controller-transmitter, thedevice is for pain management of recurring but not continuous pain, forexample, headache pain. In the external embodiment, miniaturizedreceiver-stimulator devices are implanted, but thecontroller-transmitter unit is external to the body, possibly hand-heldor worn attached to a belt or harness. The acoustic energy from theexternal controller-transmitter is coupled through the skin as well asany underlying tissues, to the implanted device. The externalcontroller-transmitter is under control of the patient. Thus, when thepatient begins to feel pain, the controller-transmitter unit is appliedand/or switched on, and certain characteristics, for example, the levelof stimulating energy and possibly the frequency or pulse duration ofthe stimulating waveform, is modified by the user, enabling the user totailor the stimulation as needed to diminish the pain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing the basics of the spinal cord anatomy.

FIG. 2 is a schematic showing the leadless stimulation system inapplication with an implantable transmitter-controller for spinal cordstimulation.

FIG. 3 is a schematic showing the leadless stimulation system inapplication with an externally applied transmitter-controller for spinalcord stimulation.

FIGS. 4 a and 4 b are block diagrams showing the components of theacoustic controller-transmitter and acoustic receiver-stimulators of thepresent invention.

FIG. 5 illustrates representative acoustic and electrical signals usefulin the systems and methods of the present invention.

FIGS. 6 a, 6 b, and 6 c are schematic illustrations showing componentsof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The systems and devices described here comprise a controller-transmitterdevice that will deliver vibrational energy and signal information toone or more implanted receiver-stimulator device(s) that will convertthe vibrational energy to electrical energy of a form that can be usedto electrically stimulate nerve tissue in the spine. The vibrationalenergy can be applied with ultrasound as a single burst or as multiplebursts or as a continuous wave with appropriate selection of thefollowing parameters:

Parameter Value Range Ultrasound frequency 20 kHz-10 MHz Burst Length(#cycles) 3-Continuous Stimulation Pulse Duration 0.1 μsec-ContinuousDuty Cycle 0-100% Mechanical Index ≦1.9

The controller-transmitter device would contain an ultrasound transduceror transducers of appropriate size(s) and aperture(s) to generatesufficient acoustic power to achieve the desired stimulation at thelocation of an implanted receiver-stimulator device. Additionally,multiple implanted receiver-stimulator devices may be placed within theregion insonified by the controller-transmitter device. Multiplereceiver-stimulator implants may function simultaneously; it is alsopossible for multiple devices to function independently, either byresponding only to a specific transmitted frequency, or through the useof a selective modulation technique such as pulse width modulation, orthrough encoding techniques such as time-division multiplexing.

A leadless pulse stimulator would be applied as follows. Using apercutaneous needle delivery technique that is used to access theepidural space, a miniaturized receiver-stimulator device disposedwithin the delivery needle is implanted into tissue or attached to thedesired location in the epidural space. Various techniques and tools forspinal access and probing of nerve tissue are commonly known. Thesecould be adapted to facilitate delivery of the receiver-stimulator tothese locations; the receiver-transmitter may incorporate means toprovide permanent attachment to the implant site including possiblyhelical coils, barbs, tines, or the like. Alternatively, thereceiver-stimulator could be implanted during a minimally invasivesurgical procedure or an open spine surgical procedure.

Functionally, the receiver-stimulator device comprises an ultrasoundtransducer to receive acoustic energy and transform it into electricalenergy, an electrical circuit to transform the alternating electricalenergy into a direct current or a pre-determined waveform, andelectrodes to transfer the electrical field energy between an electrodepair to the tissue and to the surrounding area.

Additionally, a controller-transmitter device is adapted fordirectional, vibrational energy transmission emitted by the device tointersect the implanted receiver-stimulator. In an implanted version,the controller-transmitter device containing the transmitting transduceris implanted typically just beneath the skin in a subcutaneous space. Ifnot implanted, the transducer portion of the transmitter would be placedover the skin directionally angled to the target region containing thereceiver-stimulator with acoustic gel, or other means, used for couplingthe acoustic energy to the skin.

In an alternative embodiment, the controller-transmitter device isincorporated into a device also providing conventional lead-basedelectrical stimulation, in a spinal cord stimulation system, wherein aconventional lead/electrode system would provide stimulus to directlyconnected regions of the spine using leads and transmitting vibrationalenergy to provide stimulation to regions of the spine wherereceiver-stimulators are implanted.

The controller-transmitter device would contain similar elements of mostcurrently available stimulator systems including a power source,stimulation control and timing circuitry, physiologic sensing systems;in the implanted embodiment, a system to communicate with an outsideconsole for data transmission, diagnostic, and programming functionstypically through a radiofrequency (RF) link is provided. Additionally,the controller-transmitter device would contain an ultrasound amplifierand one or more ultrasound transducers to generate acoustic energy, andtransmit such energy in the general direction of the receiver-stimulatorimplanted in the spine region. The duration, timing, and power of theacoustic energy transmission would be controlled as required, per testedparameters that are constructed for specific treatments for pain.

A single receiver-stimulator device is implanted in the epidural regionof the spine as described above for single-region stimulation;alternatively it would be possible to implant a plurality ofreceiver-stimulator devices to stimulate either simultaneously byreceiving the same transmitted acoustic energy or independently byresponding only to acoustic energy with specific characteristics (i.e.,of a certain frequency, amplitude, or by other modulation or encoding ofthe acoustic waveform) intended to energize only that specific device.This enables a much more robust utilization of site and region specificstimulation, which is not currently practical with current lead-basedimplementations whose electrode spacing is fixed on the lead setselected for use. Selecting multiple sites and regions for treatmentswould be greatly enhanced by eliminating the need to connect multipleelectrode sites to the stimulation energy source by the use of multipleleads/wires connected to the electrodes or by attempting to anticipatethe required spacing between electrodes.

These examples are representative but in no way limiting of theapplications in which an electro-acoustic stimulator may be utilized inthis invention to stimulate tissue in the spine to effect treatment ofpain.

The delivery of ultrasound energy and, therefore, electrical stimulationcould either be automatically triggered based on information receivedfrom an internal or external physiological sensor, or be based uponprogrammed settings, or be manually activated by the patient or otherindividuals. More specifically, the timing of the initiation of thedelivery and/or the duration of the delivery and/or the energy contentof the delivery and/or the information content of the delivery could bebased upon sensor information or based upon programmed settings or bemanually controlled.

Examples of such an electro-acoustic stimulation system as a spinestimulator are illustrated in FIGS. 2 and 3.

In FIG. 2, a controller-transmitter device 1 containing circuitry toprovide stimulation control and ultrasound transmission, plus means tocommunicate with an outside programmer 3 is implanted subcutaneously. Itis situated such that the directional angle of the transmittedultrasound beam would intersect the receiver-stimulator 2. An ultrasoundsignal is transmitted by this device through intervening tissue to thereceiver-stimulator device 2 containing means to receive this acousticenergy and convert it into an electrical waveform which may then beapplied to the attached electrodes. In FIG. 2, this receiver-stimulatordevice 2 is shown embedded, in this one example, in the lumbar region ofthe spine. The receiver-stimulator device 2 is shown here as a smallcylindrical or button-shaped device placed in the epidural regionsimilar to current stimulator systems. Optionally, thereceiver-stimulator 2 could be deployed into the epidural space affixedwith an attaching coil or other method. Also optionally (not shown), thereceiver-stimulator device 2 could be incorporated into a expandable orself-expanding mechanical mesh that would stay located in the tissue bymeans of spring tension similar to a stent placement in a vascularapplication but rather held in place between tissue sections of thespine.

In FIG. 3, an externally applied controller-transmitter device 41containing circuitry to provide stimulation therapy control andultrasound transmission, plus control means 42 to allow the patient oroperator to directly adjust ultrasound output based on desired therapyparameters including, at least, amplitude, pulse duration, and pulserepetition frequency, to produce effective pain relief. The externaltransmitter 41 may be handheld, or worn on the body, attached by a belt,harness, or the like. The external controller-transmitter 41 is similarto the implantable controller-transmitter device described previously,containing at the minimum an adjustable pulse/frequency generator,ultrasound amplifier, ultrasound transmitter, and battery. Optionally,the battery may be a rechargeable type. It is situated such that thedirectional angle of the transmitted ultrasound beam would intersect thereceiver-stimulator 2. An ultrasound signal is transmitted by thisdevice through intervening tissue to the receiver-stimulator device 2containing means to receive this acoustic energy and convert it into anelectrical waveform which may then be applied to the attachedelectrodes. In FIG. 3, this receiver-stimulator device 2 is shownembedded, in this one example, in the lumbar region of the spine.

FIGS. 4 a and 4 b show more details of the system described above andshown in FIG. 2. In FIG. 4 a, the controller-transmitter device 1comprises: a battery 10, one or more sensors 11, signal processingcircuitry 12, a communications module 13, a control and timing module14, an ultrasound amplifier 15, and an ultrasound transducer 16. Thebattery 10 which provides power for the controller-transmitter may be ofa type commonly used in implanted medical devices such as a lithiumiodine cell or lithium silver vanadium oxide cell made by Greatbatch,Inc. or which is optionally a rechargeable battery. One or more sensors11 are used to detect physiological parameters. Suitable sensors areknown for the detection of electrical activity, temperature, motion,pressure, and the like. These sensors are connected to signal processingcircuitry 12 and optionally used by the circuitry to adjust delivery ofstimulation therapy or to communicate diagnostic information from thesensors. The communications module 13 provides a data path to allow thephysician to set device parameters and to acquire diagnostic informationabout the patient and/or the device. The data path may be by an RFcommunication link, magnetic coupling, ultrasound pulses, or the like,and would communicate to and from an external unit 3. Device parameterswould be used by the control and timing module 14. Device parameterswould include adjustments to transmissions, such as power amplitude,pulse duration, duty cycle, and the like. The control and timing module14 uses device parameters in conjunction with the acquired physiologicaldata to generate the required control signals for the ultrasoundamplifier 15, which in turn applies electrical energy to the ultrasoundtransducer 16, which in turn produces the desired acoustic beam. Thecontroller-transmitter device 1 is encased in a hermetically sealed case17 constructed of a bio-compatible material, similar to current SCSdevices.

Referring to FIG. 4 b, the receiver-stimulator device 2, implanted inthe path of the acoustic beam at the location where electricalstimulation is desired, contains an ultrasound transducer 20, anelectrical circuit 21, and electrodes 22. Ultrasound transducer 20,typically made of a piezoelectric ceramic material, a piezoelectricsingle crystal, or piezoelectric polymer or copolymer films, interceptsa portion of the transmitted acoustic energy and converts it into anelectrical current waveform from the original alternating nature of theapplied ultrasound pressure wave. This electrical signal is applied toan electrical circuit 21 which may be one of a type commonly known as anenvelope detector, and which may have one of many known circuitconfigurations; for example, a full-wave rectifier, a half-waverectifier, a voltage doubler or the like. Electrical circuit 21 producesa voltage pulse with amplitude proportional to the amplitude of thetransmitted ultrasound burst and with a pulse length generally equal tothe length of the transmitted burst. The circuit 21 may also havedifferent configurations and functionalities, and provide output signalshaving characteristics other than a pulse. This signal is then appliedto electrodes 22, which are typically made of platinum,platinum-iridium, gold, or the like. These may be incorporated onto theouter surface of the device, and thus in direct contact within theepidural layer or within close proximity of nerves or nerve fibers whichare to be treated by stimulation. Alternatively, the electrodes 22 areconnected via wires to a main body that consists of the transducer 20and electrical circuit 21 and the electrodes 22 are adapted to beshapeable, malleable configurations that conform to regions of the spineas flexible wraps or the like or that could be placed on the dura.Electrodes may be adapted that are round, long, segmented, etc. toincrease surface area or to control current density at the electrode.Electrodes may be placed on opposing sides of the tissues or in linearalignment with the tissue or in any arrangement suitable for the sizeand location of the spine and the targeted spine stimulation site. Thereceiver-stimulator device 2 is also enclosed within a sealed case 23 ofbiologically compatible material

Referring also to previously described FIGS. 4 a and 4 b, FIG. 5provides detail representing exemplary acoustic and electrical signalsof the present system. FIG. 5 first depicts a train of electricalstimulation pulses 31 which have a desired width and are repeated at adesired interval. The controller-transmitter device 1 produces acoustictransmissions 32, for the desired stimulation pulse width and repeatedat the desired stimulation pulse interval, which are emitted from theultrasound transducer 16. Below the waveform 32 is shown an enlargement33 of a single acoustic burst. This burst again has a desired width, adesired oscillation frequency F=1/t, and also a desired acousticpressure indicated by the peak positive pressure P+ and peak negativepressure P−. The acoustic pressure wave, when striking the receivingtransducer 20 of the receiver-stimulator device 2 generates anelectrical signal 34 having frequency and burst length matching that ofthe transmitted waveform 33 and amplitude proportional to thetransmitted acoustic pressure (˜+/−P). This electrical waveform is thenrectified and filtered by the circuit 21 producing the desired pulse 35with length equal to the burst length of the transmitted waveform 33 andamplitude (V_(PULSE)) proportional to the amplitude of the electricalsignal 34. Thus, it can be seen that it is possible in this example tovary the stimulation rate by varying the time between ultrasound bursts,to vary the duration of any one stimulation pulse by varying theduration of the ultrasound burst, and to vary the amplitude of thestimulation pulse by varying the amplitude of the transmitted ultrasoundwaveform. Circuit 21 could be configured to produce a direct current(DC) output or an alternating current (AC) output, or an output with anyarbitrary waveform. Varying the use of signal information within theultrasound transmission for pulse duration, pulse amplitude, and dutycycle would result in any type of burst sequencing or continuousdelivery waveform effective for brain stimulation. Using signalinformation in the ultrasound transmission the resultant waveshape maybe a square wave, triangle wave, biphasic wave, multi-phase wave, or thelike.

In practice, the amount of acoustic energy received by the implantedreceiver-stimulator device will vary with ultrasound attenuation causedby loss in the intervening tissue, with spatial location of thereceiver-stimulator device with respect to the transmitted ultrasoundbeam, as such a beam is typically non-uniform from edge-to-edge, andpossibly with orientation (rotation) of the receiver-stimulator devicewith respect to the first. Such variation would affect the amplitude ofthe stimulating pulse for a given ultrasound transmit power (acousticpressure amplitude). This limitation can be overcome by adjusting theultrasound transmit power until the resultant stimulation waveform isconsistent, a technique similar to that used currently to determinestimulation thresholds at the time of cardiac pacemaker implantation.Another approach would be to automatically adjust using sensing andlogic within the first device. The first device would periodically sensethe electrical output of the receiver-stimulator device and adjust powertransmission accordingly to compensate for any change in the systemincluding relative movement between the transmitting and receivingdevices. Yet another embodiment for overcoming this limitation is wherethe transducer incorporated into the receiver-stimulator device isomni-directional in its reception capability. For example, to improveomni-directional sensitivity, the transducer may be spherical in shapeor have specific dimensional characteristics relative to the wavelengthof the transmitted ultrasound. Alternatively, multiple transducers aredisposed at appropriate angles to reduce or eliminate the directionalsensitivity of the device.

FIGS. 6 a through 6 c illustrate two embodiments of a small implantablereceiver-stimulator of a cylindrical profile, suitable perhaps forplacement by stylet or by injection through a hypodermic needle. FIG. 6a shows in plan view and 6 b in perspective view such areceiver-stimulator 2 having a hollow, cylindrical ultrasound transducer71, a circuit assembly 72 comprising the detector, and two electrodes 73at either end of the assembly. It can be appreciated that any number ofelectrodes may be adapted to this embodiment. The transducer 71 would bemade of an appropriate piezoelectric ceramic material, having twoelectrical activity contacts deposited on the outer and inner surfacesof the cylinder, respectively. The transducer and circuit would beencapsulated in an electrically insulating but acoustically transparentmedium 74. The transducer 71 would be of a rigid piezoelectric material,typically a piezo-ceramic with electrodes deposited on the outer andinner surfaces of the cylinder. The circuit assembly 72 may befabricated using known surface-mount or hybrid assembly techniques, uponeither a fiberglass or ceramic substrate. Stimulation electrodes 73would be fabricated of material commonly used in implanted electrodes,such as platinum, platinum-iridium, or the like. Necessary electricalwiring between the transducer, circuit board, and electrodes is notshown in these drawings. Typical dimensions of such a device would be1.5 cm in length and 1.5 mm in diameter, and preferably smaller.Multiple electrodes could be adapted as appendages to the embodiment(not shown) or incorporated into fixation elements such as helicalscrews or barbs (not shown).

As shown in FIG. 6 c, by using hybrid circuit techniques it may bepossible to further miniaturize the circuit assembly 72 such that itwould fit inside the hollow interior of the transducer 71. This wouldhave the benefit of substantially reducing the length of the finisheddevice.

While exemplary embodiments have been shown and described in detail forpurposes of clarity, it will be clear to those of ordinary skill in theart from a reading of the disclosure that various changes in form ordetail, modifications, or other alterations to the invention asdescribed may be made without departing from the true scope of theinvention in the appended claims. For example, while specific dimensionsand materials for the device have been described, it should beappreciated that changes to the dimensions or the specific materialscomprising the device will not detract from the inventive concept.Accordingly, all such changes, modifications, and alterations should beseen as within the scope of the disclosure.

What is claimed is:
 1. A system for stimulating the spinal cord, saidsystem comprising: an acoustic controller-transmitter configured totransmit acoustic energy, wherein the controller-transmitter comprisesacoustic transducers disposed in a housing and one or more sensorsdisposed on an external surface of the housing; and an implantableacoustic receiver-stimulator having a stimulation electrode assemblyadapted to be in direct contact with epidural tissue, wherein thereceiver-stimulator is configured to receive and convert the acousticenergy into an electrical stimulation output delivered to the epiduraltissue by the stimulation electrode assembly, wherein the electricalstimulation output has at least one of pulse amplitude, pulse duration,duty cycle, and timing based on energy and signal information includedin the generated acoustic energy; wherein the controller-transmitter isconfigured to sense the electrical stimulation output of thereceiver-stimulator using one or more of the sensors and adjust acousticenergy transmission from the controller-transmitter accordingly in orderto compensate for changes in electrical stimulation output of thereceiver-stimulator.
 2. The system as in claim 1, wherein thereceiver-stimulator comprises an acoustic receiver which receivesacoustic energy and generates alternating current, means for convertingthe alternating current to a pre-determined waveform, and the electrodeassembly adapted to deliver the pre-determined waveform to stimulate thespine.
 3. The system as in claim 2, wherein the implantablereceiver-stimulator is adapted to be implanted and secured at apredetermined spine stimulation site, said predetermined spinestimulation site being selected to treat peripheral nerves from thegroup consisting of trigeminal ganglion or ganglia, one or moretrigeminal nerves, one or more branches of a trigeminal nerve, or one ormore branches of any of these neural structures.
 4. The system as inclaim 3, wherein the implantable receiver-stimulator is adapted to beplaced and secured to stimulate nerves effective in alleviating pain asa therapeutic treatment.
 5. The system as in claim 4, further comprisingat least one additional receiver-stimulator device.
 6. The system as inclaim 5, wherein the system is programmed to activate thereceiver-stimulator devices sequentially.
 7. The system as in claim 5,wherein the system is programmed to activate the receiver-stimulatordevices simultaneously.
 8. The system as in claim 3, further comprisingat least one additional receiver-stimulator device.
 9. The system as inclaim 8, wherein the system is programmed to activate thereceiver-stimulator devices sequentially.
 10. The system as in claim 8,wherein the system is programmed to activate the receiver-stimulatordevices simultaneously.
 11. The system as in claim 1, wherein thecontroller-transmitter comprises a power source, control and timingcircuitry to provide a stimulation signal, means for converting thestimulation signal to an acoustic energy signal, and means fortransmitting the acoustic energy signal to the receiver-stimulator. 12.The system as in claim 11, wherein control circuitry includes one ormore means to adjust the electrical stimulation output with one or moreparameters chosen from pulse amplitude, pulse duration, duty cycle, ortiming.
 13. The system as in claim 11, wherein thecontroller-transmitter is adapted to be implantable.
 14. The system asin claim 1, further comprising at least one additionalreceiver-stimulator device.
 15. The system as in claim 14, wherein thesystem is programmed to activate the receiver-stimulator devicessequentially.
 16. The system as in claim 14, wherein the system isprogrammed to activate the receiver-stimulator devices simultaneously.17. The system as in claim 1, adapted to transmit and receive acousticenergy wherein the frequency of the acoustic energy is between 20 kHzand 10 MHz, the burst length is between 3 cycles and a continuous burst,the duty cycle is between 0.01% and 100.00%, and the mechanical index isless than 1.9.